Structural and Dynamic Investigation of [EMIM]+[PF6]-Electrolyte: An Atomistic Simulation

Publish Year: 1394
نوع سند: مقاله کنفرانسی
زبان: English
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ELECTROCHEMISTRY011_263

تاریخ نمایه سازی: 5 بهمن 1395

Abstract:

Ionic Liquids (ILs) have received a great deal of attention in recent years due to their potential in gas storage, electrodeposition, biocatalysis, lubricant, and as electrolyte. Wide electrochemical window, excellent thermal stability, low vapor pressure, [1, 2] and their other unique featurescause these materials find remarkable applications in electrochemistry. [2, 3] The present research involves the structural and dynamic properties of IL consist of 1-ethyl, 3-methyl imidazolium cation and hexaflourophosphate anion ([EMIM]+[PF6]-) performed by molecular dynamics simulation.Simulation Details 300 ion pairs of [EMIM]+[PF6]- were located and simulated in a periodic box. A 2 ns NPT production run was performed at 373 Kand 1 atm, with 1 fs time step and 12 Å cutoff distance. Hoover thermostat and barostate were applied to the system. The forcefield parameters were taken from Lopes et al. [4]. Results and Discussion Mean square displacement (MSD) is related to the self-diffusion coefficient of ions by the well-knownEinstein equation. Calculated diffusion values are 5.19×10-11, 2.4×10-11, and 3.79×10-11 m2/s for cation,anion, and IL, respectively. Cation has higher diffusion value due to its lower charge density. Analyzing atomistic MSD of cation showed that alkylchain atoms possess higher MSD values than ring atoms(Fig. 3), because of their high mobility and low spatial hindrance. Anion has stronger attraction with C_R and C_M (shownin Fig. 1) in comparison with tail and other atoms of cation. Thus, it is reasonable to consider the anion wasplaced in the region between methyl tail and C_R head of the ring. As it can be obvious in Fig. 1. Cation-anion RDF has been applied to characterize thethe ability of hydrogen bonding. Figure 4 shows a clear strong interaction between H_R and F, which can be considered as a hydrogen bond. This correlation causesstrong intermolecular attraction reducing the ions diffusion. Conclusion A molecular level description of [EMIM]+[PF6]- wasprovided which considered structural and dynamic properties of IL. [EMIM]+ cation has higher diffusion values than anion, due to its lower charge density. TheRDF plots showed anion placed near the ring of cation. Moreover, the results of hydrogen correlation showed the hydrogen bond between H_R of cation and F of anion.

Authors

B Sadeghi Moghadam

Department of Chemical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

f Moosavi

Department of Chemistry, Ferdowsi University of Mashhad, Mashhad, Iran

M.T Hamed Mosavian

Department of Chemical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

m Razmkhah

Department of Chemical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran